function [x_next, y_next] = f2(x, y, a, b, c, d)
% MNFM2 映射
%   x(k+1) = a * x(k)/(1 + x(k)^2) + b*sin(c*cos(y(k))*x(k)) + d
%   y(k+1) = y(k) + x(k)

    x_next = a * x / (1 + x^2) ...
           + b * sin(c * cos(y) * x) ...
           + d;

    y_next = y + x;
end

